GTKmm + Cmake + Cpp + VS19 issue on Generating

Hi there… I tried to start a cmake Project in VS19, wanting to use gtkmm(4) with C++.

So, this is my CMakeList:

cmake_minimum_required (VERSION 2.6)

project ("Tester")

set(CMAKE_CXX_STANDARD 20) 
set(CMAKE_CXX_STANDARD_REQUIRED ON) 
set(CMAKE_CXX_EXTENSIONS OFF)

find_package(PkgConfig REQUIRED)
pkg_check_modules(GTK REQUIRED gtkmm-4.0)

include_directories(${GTK_INCLUDE_DIRS}) 
link_directories(${GTK_LIBRARY_DIRS}) 
add_definitions(${GTK_CFLAGS_OTHER})

add_executable (Tester "Tester.cpp" "Tester.h")
target_link_libraries(Tester${GTK_LIBRARIES})

As compiler, it doesn´t matter if i use msvc_x64 or clang_cl_x64… I always get over 100 Errors about unknown types, tokens and base classes in surface.h


(see attachment)

I also tried different Versions of CXX, instead of 20 i tried everything from 11…20.

So, can someone lead me into the correct Direction on how to use gtkmm4, with Visual Studio 2019, cmake and Cpp?